How to fix RAID1 array

[Gavin McCullagh]

Hi,

On Thu, 07 Jan 2010, Todd O'Bryan wrote:

> I have my student home folders on a RAID1 array. One of the hard
> drives seems to have become corrupted--I'm getting Buffer IO errors.

Ouch.  Is that a hardware RAID card or an MD linux software RAID one?

> Is the hard drive definitely bad so I should get a new one, or should
> I try reformatting it and seeing if it works again?

Could you paste a selection of the errors into an email?  It may not be
easy to tell, but it helps to have the full detail.

> Either way, how do I do that? Is there a way to run the partitioner
> part of the alternate install CD without running the whole installer?
> Will the RAID array automatically pick up the reformat of the current
> drive or a new drive if I have to get one?

If it's hardware RAID, you generally just determine which disk is dead,
replace it and let it resync (depending on the exact detail you may need to
shutdown or not).  If you're using software RAID you'd probably need to
work out which is the bad disk, take the server down, replace the disk,
boot back up, create identical sizes partitions on the new disk and add
those partitions to the existing RAID arrays.  Linux will then sync them
with the system running.

> Anyone got a link to TFM that I should R before I attempt this?

	http://tldp.org/HOWTO/Software-RAID-HOWTO.html
	man mdadm

Commands like:

	ls -l /dev/md*
	mdadm --help
	sudo mdadm --detail /dev/md0
	mdadm /dev/md0 --add /dev/sdb1

will likely be what you'll need.  Needless to say, be very careful what you
do.

Gavin